The present invention is directed to compounds potentially useful in controlling insects. More particularly, the present invention is directed to active chromene compounds which are effective in inhibiting the effects of juvenile hormone in insects.
Of the various chemical compounds which have been employed in the prior art as insecticides for controlling insects, many of such prior art compounds have also been found to be harmful to humans and other animal life. In addition, many species of insect pests have developed a resistance and even immunity to available insecticides.
Alternative prior art methods for controlling insects have included the use of hormones, which interfere with the development of insects. Although such hormones have the advantage of apparently being harmless to other animals, their use is generally limited to application relatively late in the insect life cycle, after the insect has already produced its undesirable pest effect.
The endocrine systems of insects secrete a certain hormone known as juvenile hormone which functions to control the biological activities of metamorphosis, reproduction, diapause and sex attractant production. In particular, juvenile hormone functions initially to maintain the young developing insect in an immature condition until it has developed to the point where it is ready to molt to the adult form. When maturation of the insect begins, the body ceases to secrete juvenile hormone until after the insect has passed into the adult form, at which time secretion of juvenile hormone recommences in order to promote the development of the sex organs.
The forms in which juvenile hormone are known to occur in nature are discussed in the following publications: Trautmann et al., Z. Naturforsch, 29C 161-168 (1974); Judy et al., Proc. Nat. Acad. Sci. USA, 70, 1509-1513 (1973); Roller et al., Angew. Chem. Int. Ed. Eng., 6, 179-180 (1967); Meyer et al., Proc. Nat. Acad. Sci. USA, 60, 853-860 (1968); Judy et al., Life Sci., 13, 1511-1516 (1973); Jennings et al., Life Sci., 16, 1033-1040 (1975); and Judy et al., Life Sci., 16, 1059-1066 (1975).
In accordance with the present invention, it has been discovered that the lipid extract of the common bedding plant, Ageratum, contains two active compounds: (1) 6,7-dimethoxy-2,2-dimethyl-3-chromene; and (2) 7-methoxy-2,2-dimethyl-3-chromene; each of which is effective to inhibit the effects of juvenile hormone in insects. Both compounds have been described in the literature: A. R. Alertsen "Ageratochromene, a Heterocyclic Compound from the Essential Oils of some Agertaum Species", Acta Chem. Scand. 9 (1955) No. 10, pp. 1725-1726; R. Huls "Syntheses De Chromenes Substitutes", Bull. Soc. Chim. Belg., 67 (1958), pp. 22-32; R. Livingston et al., J. Chem. Soc., p. 1509 et seq. (1957); and T. R. Kasturi et al., Tetrahedron Lett. 27 (1967), p. 2573 et seq.
These and related chromene compounds inhibit the effects of Juvenile hormone, during early development of the insect and after reaching adulthood when the sex organs are undergoing development. By so inhibiting the effects of juvenile hormone, the maturing insect which has been treated with the present compounds is caused to die within a short time of such treatment. In addition, the ability of a treated insect to reproduce is prevented. The compounds of the present invention have also been found to interrupt embryogenesis in insect eggs, to induce diapause in insects and to prevent sex pheromone secretion in insects. The present compounds may be applied by suitable means including topically, orally or in a vapor state as a fumigant.